Abstract
The FDA has approved the first drug for locally advanced or metastatic pheochromocytoma and paraganglioma—a radioactive isotope of iodine called iobenguane I 131 that's absorbed by tumor cells. Twenty-five percent of patients who received it reduced their use of antihypertensive drugs by half for at least 6 months.
The FDA has approved iobenguane I 131 (Azedra; Progenics Pharmaceuticals) for locally advanced or metastatic pheochromocytoma and paraganglioma. The drug, which delivers a radioactive isotope of iodine to the tumors, is the first treatment greenlighted for these cancers.
About 100 to 200 people in the United States are diagnosed with malignant pheochromocytoma or paraganglioma each year. The tumors release hormones, such as epinephrine, driving up blood pressure and increasing stroke and heart attack risk.
Researchers have tested several potential therapies, including a different form of iobenguane, but none had received approval for patients with locally advanced or metastatic tumors. The newly approved drug provides a more concentrated dose of the radioisotope than the previously tested forms. In many patients, pheochromocytoma and paraganglioma cells carry norepinephrine transporters that allow the tumors to absorb it.
“It's a way to give very targeted radiation therapy to the tumors,” says Rebecca Sippel, MD, of the University of Wisconsin–Madison.
The FDA's decision was based on data from 68 patients in a single-arm, phase IIb trial. With the drug, 25% of the patients halved their use of antihypertensive medications for at least 6 months. In addition, tumors responded to the drug in 22% of the patients.
Structural formula for iobenguane I 131
“The FDA approval is huge,” says Sippel. The treatment is “not a cure for the disease, but it decreases hormone production and improves symptom burden for patients.”
In the trial, grade 3 or 4 side effects that occurred in at least 10% of the patients included lymphopenia, neutropenia, thrombocytopenia, fatigue, and nausea. These side effects were similar to those of other radiotherapeutic agents. In addition, a small number of patients developed myelodysplastic syndrome, notes Lauren Fishbein, MD, PhD, of the University of Colorado School of Medicine in Aurora. “That will need further study because it can be serious.”
Nonetheless, she says, the drug's ability to shrink tumors and reduce the need for antihypertensive medications “is a big step in the right direction” for a subset of patients. –Mitch Leslie
For more news on cancer research, visit Cancer Discovery online at http://cancerdiscovery.aacrjournals.org/CDNews.
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